Overhead door openers are in widespread use, primary for opening garage doors. They consist of a drive motor, a chain or cable to which is attached a trolley with a control arm that is adapted to be secured to an overhead door. All overhead door openers have some form of reversing mechanism which stops the drive motor when the door reaches an open position or when the door reaches a closed position. If, for some reason, the reversing mechanism is not activated as the door reaches the open position or the closed position, the motor will keep running even though the door is fully open or fully closed. Unless someone discovers the problem and shuts the motor off, the motor will sustain damage. There are various reasons why the reversing mechanism may not be activated. One such reason is a loose chain or cable which skips over the reversing mechanism.